Some work vehicles, such as end loaders, must change their directions of movement frequently. To do this, wheel or live axle brakes are generally used to first bring the vehicle to a stop. When this is done frequently, the brakes become overheated.
This has sometimes been resolved by placing the brakes inside an axle housing, where the heat generated by brake friction is removed from the brake by an axle lubricating bath. The lubricant spreads the heat over the entire interior surface of the axle housing, whereupon thermal conduction through the walls of the axle housing heat the exterior surface of the axle housing and provide increased surface area for heat to be convected away by ambient air.
In some instances, however, convection to and from the axle housing surfaces is insufficient to remove braking heat rapidly enough, and the axle lubricant consequently becomes excessively hot (e.g., above 300 degrees Fahrenheit). This is injurious not only to the lubricant itself (accelerating oxidation and breakdown), but also to the bearings and seals associated with the axle shaft.
Typically, the brake is a wet multiple disk brake; “wet”, because the disks rotate through a bath of lubricating oil. As the multiple brake disks rotate through the lubricating oil, braking heat is transferred from the disks to the lubricating oil.
The temperature of the lubricating oil consequently increases, and some of the heat within the lubricating oil is transferred to the axle shaft and to the axle housing. The axle shaft and axle housing are of limited size and mass and, hence, of limited heat capacity. Therefore, their temperatures begin to approach (under the duty cycle of frequent stops characteristic of a loader) the temperature of the lubricating oil because ambient air typically does not convect heat from the axle housing as rapidly as the brake convects heat into the lubricating oil. It is therefore necessary to actively cool the lubricating oil.
One way to actively cool the lubricating oil is to add a cooling loop to an axle assembly and pump hot lubricating oil through a fan-cooled radiator. However, in extremely cold operating conditions, especially during start-up, it may be undesirable to attempt to circulate the lubricating oil to the axle assembly. Such circulation of highly viscous lubricating oil may result in the formation of “hot spots” in the axle assembly, causing degradation of axle assembly components.
It would be advantageous to provide an apparatus to selectively provide lubricating oil to the axle assembly to protect axle assembly components.